Study On Preparation And Performance Of Porous Ceramics With Directional Pore Structure

The development of high-speed aircraft and high-temperature reactor urgently require insulation materials with high temperature resistance,low thermal conductivity,and high mechanical strength.Porous ceramics not only have the excellent characteristics of traditional ceramics such as high temperature and high-pressure resistance,good thermal shock resistance and corrosion resistance,but also have the characteristics of lightweight,low thermal conductivity,high specific surface area,and high permeability.It is widely used in thermal insulation.The pore structure and performance of porous ceramics are closely related,and different preparation processes can obtain different microstructures.In this paper,through the simulation calculation by FLUENT software,it is found that the material with directional pore structure has extremely low effective thermal conductivity in certain direction.The effective thermal conductivity of the material is related to the solid phase thermal conductivity and porosity,and the directional pore structure can enhance the mechanical strength of the hole direction.In this article,the unique fiber structure of bacterial cellulose?BC?can be used to obtain a stable ceramic slurry with low solid content.Porous mullite,porous anorthite,and mullite/anorthite composite porous ceramics with directional pore structure were prepared by freeze-drying method.The porosity,microstructure,and thermal conductivity of the samples were analyzed by Archimedes drainage method,scanning electron microscope?SEM?,and Hot Disk thermal constant analyzer.The effects of solid content and freezing temperature on porosity,thermal conductivity,and compressive strength were investigated.The experimental results showed that changing the solid content and freezing temperature can produce directional porous mullite with a porosity of 67.6%to 91.1%.The highest compressive strength is 8.06MPa,and the lowest thermal conductivity is 0.0867W/m·K while the porosity is 91.9%.Mullite whiskers with an aspect ratio of about 20 were generated in situ during the sintering process,so that the high porosity ceramics had good mechanical properties.Using Al₂O₃,Si O₂ and Ca CO₃ as raw materials,directional porous anorthite with porosity between 75.1%and 90.5%can be obtained through the same process route,and low thermal conductivity of 0.1475 W/m·K was maintained at 30wt%solid content.Kaolin and Al?OH?₃,Ca?OH?₂ are used as raw materials to prepare directional composite porous ceramics.The lowest thermal conductivity of the composite phase porous ceramic is 0.0349W/m·K,and the thermal conductivity can be kept at 0.0900W/m·K when the compressive strength reaches7.14MPa.